originally an Indian belonging to one phratry could marry a woman belonging to the other only.  Subsequently the line was drawn less strictly, but still no Indian was allowed to marry a squaw of his own clan, though there might be no blood, relationship between them.  If an Algonkin married a girl of his clan he committed a crime for which his nearest relatives might put him to death.  This law has prevailed widely among the wild races in various parts of the globe.  McLennan, who first called attention to its prevalence and importance, called it exogamy, or marrying-out.

What led to this custom is not known definitely; nearly every anthropologist has his own theory on the subject.[134] Luckily we are not concerned here with the origin and causes of exogamy, but only with the fact of its existence.  It occurs not only among barbarians of a comparatively high type, like the North American Indians, but among the lowest Australian savages, who put to death any man who marries or assaults a woman of the same clan as his.  In some Polynesian islands, among the wild tribes of India as well as the Hindoos, in various parts of Africa, the law of exogamy prevails, and wherever it exists it forms a serious obstacle to free choice—­i.e., free love, in the proper sense of the expression.  As Herbert Spencer remarks,

“The exogamous custom as at first established [being connected with capture] implies an extremely abject condition of women; a brutal treatment of them; an entire absence of the higher sentiments that accompany the relations of the sexes.”

While exogamy thwarts love by minimizing the chances of intimate acquaintance and genuine courtship, there is another form of sexual taboo which conversely and designedly frustrates the tendency of intimate acquaintance to ripen into passion and love.  Though we do not know just how the horror of incest arose, there can be no doubt that there must be a natural basis for so strong and widely prevalent a sentiment.  In so far as this horror of incest prevents the marriage of near relatives, it is an obstacle to love that must be commended as doubtless useful to the race.  But when we find that in China there are only 530 surnames, and that a man who marries a woman of the same surname is punished for the crime of “incest”; that the Church under Theodosius the Great forbade the union of relatives to the seventh degree; that in many countries a man could not wed a relative by marriage; that in Rome union with an adopted brother or sister was as rigidly forbidden as with a real sister or brother;—­when we come across such facts we see that artificial and foolish notions regarding incest must be added to the long list of agencies that have retarded the growth of free choice and true love.  And it should be noted that in all these cases of exogamy and taboos of artificial incest, the man’s liberty of choice was restricted as well as the woman’s.  Thus our cumulative evidence against the Darwin-Westermarck theory of free choice is constantly gaining in weight.